A direct injection gas (DIG) engine is an engine in which a gaseous fuel, such as natural gas, is injected into a cylinder at high pressure while combustion in the cylinder from a diesel pilot is already underway. DIG engines operate on the gaseous fuel, and the diesel pilot provides ignition of the gaseous fuel. Another type of engine that uses more than one fuel is typically referred to as a dual-fuel engine, which uses a low-pressure gaseous fuel such as natural gas that is mixed at relatively low pressure with intake air admitted into the engine cylinders. Dual-fuel engines are typically configured to operate with liquid fuel such as diesel or gasoline at full power. The gaseous fuel is provided to displace a quantity of liquid fuel during steady state operation. The air/gaseous fuel mixture that is provided to the cylinder under certain operating conditions is compressed and then ignited using a spark, similar to gasoline engines, or using a compression ignition fuel, such as diesel, which is injected into the air/gaseous fuel mixture present in the cylinder.
In dual fuel engines, the gaseous fuel is stored in a pressurized state in a pressure tank, from which it exits in a gaseous state before being provided to the engine. In DIG engines, however, the gaseous fuel is stored in a liquid state at low pressure, such as atmospheric pressure, and at low, cryogenic temperatures in a liquid storage tank. After exiting the liquid storage tank, the liquefied gaseous fuel needs to be brought to a gaseous state before or when it is provided to the engine cylinders.
Conventional cryogenic pumps (e.g., a reciprocating piston pump) employ an intermittent pump operation (i.e., a start-stop operation) and may be used in DIG systems to pressurize the liquid natural gas (LNG). However, the high pressure and dynamic loads involved may contribute to a reduced life of the cryogenic pump. Therefore, systems using a high pressure cryogenic pump may incur unwanted downtime and maintenance costs.
International Patent Application WO2013047574 A1, titled, “Direct fuel injection diesel engine apparatus” (“the '574 Application”). The '574 Application is directed to a direct-injection diesel engine system that uses a cryogenic liquid fuel, such as liquefied natural gas. According to the '574 Application, the cold high-pressure cryogenic liquid fuel is pressurized by a booster pump installed in a fuel supply system for cryogenic liquid fuel. The direct fuel injection diesel engine apparatus uses high-pressure natural gas obtained by vaporizing LNG as an engine fuel, and burns the engine fuel with intake air pressurized by a supercharger, comprising a booster pump which pressurizes low-pressure LNG introduced from an LNG tank.
In the '574 Application, the LNG is provided in an LNG fuel feeding system which feeds and injects the high-pressure natural gas into a cylinder of a direct fuel injection diesel engine. A cold energy recovery heat exchanger cools a heating medium through heat exchange between the heating medium circulating in a closed circuit and high-pressure LNG pressurized by the booster pump. An air cooling heat exchanger cools atmospheric air which is taken in and introduced into the supercharger through heat exchange with the heating medium at a downstream portion of the cold energy recovery heat exchanger and/or intake air after compression by the supercharger. Such a configuration uses a high pressure booster pump to pressurize the LNG introduced from the LNG tank. These and other shortcomings of the prior art are addressed by the present disclosure.